If you want solid reliability, Debian is where you might want to start. Particularly on an older PC where the hardware should be well supported. Make a live install image USB boot drive and see if you like it before you decide.
Debian is all about stability, at the cost of having less recent software. For newer versions of the desktop environments you could try live boots of KDE Neon and Pop!_OS as well.
If you want to keep using networkd, you might want to consider if multiple interfaces are causing the wait. NM doesn't care, but networkd gives more granular options for dependencies. If you have wired and wireless and only one in use the systemd-networkd-wait-online.service waits for a timeout period. You can find lots of info on it related to boot delays with that service.
Try the --any switch on the systemd-networkd-wait-online.service launch configuration. This will tell the wait-online service that any single routable interface is enough, you don't need them all.
Run:
sudo systemctl edit systemd-networkd-wait-online.service
That adds the override.conf for the service. Add these lines:
The other possibility is if you have virtual .netdev devices configured (VPN, bridging, etc) and some of them are not essential for the machine to be online, you can set RequiredForOnline=no on the ones that aren't essential.